Biodegradation of Aniline by a Newly Isolated Delftia sp. XYJ6

Enzyme-linked carbon nanotubes as biocatalytic tools to degrade and mitigate environmental pollutants

A wide array of organic compounds have been recognized as pollutants of high concern due to their controlled or uncontrolled presence in environmental matrices. The persistent prevalence of diverse organic pollutants, including pharmaceutical compounds, phenolic compounds, synthetic dyes, and other hazardous substances, necessitates robust measures for their practical and sustainable removal from water bodies. Several bioremediation and biodegradation methods have been invented and deployed, with a wide range of materials well-suited for diverse environments. Enzyme-linked carbon-based materials have been considered efficient biocatalytic platforms for the remediation of complex organic pollutants, mostly showing over 80% removal efficiency of micropollutants. The advantages of enzyme-linked carbon nanotubes (CNTs) in enzyme immobilization and improved catalytic potential may thus be advantageous for environmental research considering the current need for pollutant removal. This review outlines the perspective of current remediation approaches and highlights the advantageous features of enzyme-linked CNTs in the removal of pollutants, emphasizing their reusability and stability aspects. Furthermore, different applications of enzyme-linked CNTs in environmental research with concluding remarks and future outlooks have been highlighted. Enzyme-linked CNTs serve as a robust biocatalytic platform for the sustainability agenda with the aim of keeping the environment clean and safe from a variety of organic pollutants.

Retrospect and prospect of aerobic biodegradation of aniline: Overcome existing bottlenecks and follow future trends

Aniline is a highly bio-toxic industrial product, even at low concentrations, whose related wastewater has been flowing out worldwide on a large scale along with human production. As a green technology, aerobic biological treatment has been widely applied in industrial wastewater and exhibited various characteristics in the field of aniline wastewater. Meanwhile, this technology has shown its potential of synchronous nitrogen removal, but it still consumes energy badly. In the face of resource scarcity, this review comprehensively discusses the existing research in aerobic biodegradation of aniline wastewater to find out the developmental dawn of aerobic biological treatment. Primarily, it put forward the evolution history details of aniline biodegradation from pure culture to mixed culture and then to simultaneous nitrogen removal. On this basis, it presented the existing challenges to further expand the application of aerobic biotechnology, including the confusions of aniline metabolic mechanism, the development of co-degradation of multiple pollutants and the lack of practical experience of bioreactor operation for aniline and nitrogen removal. Additionally, the prospects of the technological shift to meet the needs of an energy-conserving society was described according to existing experiences and feasibility. Including but not limiting to the development of multifunctional bacteria, the reduction of greenhouse gases and the combination of green technologies.

Recent advances in carbon nanotubes-based biocatalysts and their applications

Enzymes have been incorporated into a wide variety of fields and industries as they catalyze many biochemical and chemical reactions. The immobilization of enzymes on carbon nanotubes (CNTs) for generating nano biocatalysts with high stability and reusability is gaining great attention among researchers. Functionalized CNTs act as excellent support for effective enzyme immobilization. Depending on the application, the enzymes can be tailored using the various surface functionalization techniques on the CNTs to extricate the desirable characteristics. Aiming at the preparation of efficient, stable, and recyclable nanobiocatalysts, this review provides an overview of the methods developed to immobilize the various enzymes. Various applications of carbon nanotube-based biocatalysts in water purification, bioremediation, biosensors, and biofuel cells have been comprehensively reviewed.

Stable-isotope probing coupled with high-throughput sequencing reveals bacterial taxa capable of degrading aniline at three contaminated sites with contrasting pH

The biodegradation of aniline is an important process related to the attenuation of aniline pollution at contaminated sites. Aniline contamination could occur in various pH (i.e., acidic, neutral, and alkaline) environments. However, little is known about preferred pH conditions of diverse aniline degraders at different sites. This study investigated the active aniline degraders present under contrasting pH environments using three aniline-contaminated cultures, namely, acidic sludge (ACID-S, pH 3.1), neutral river sediment (NEUS, pH 6.6), and alkaline paddy soil (ALKP, pH 8.7). Here, DNA-based stable isotope probing coupled with high-throughput sequencing revealed that aniline degradation was associated with Armatimonadetes sp., Tepidisphaerales sp., and Rhizobiaceae sp. in ACID-S; Thauera sp., Zoogloea sp., and Acidovorax sp. in NEUS; Delftia sp., Thauera sp., and Nocardioides sp. in ALKP. All the putative aniline-degrading bacteria identified were present in the "core" microbiome of these three cultures; however, only an appropriate pH may facilitate their ability to metabolize aniline. In addition, the biotic interactions between putative aniline-degrading bacteria and non-direct degraders showed different characteristics in three cultures, suggesting aniline-degrading bacteria employ diverse survival strategies in different pH environments. These findings expand our current knowledge regarding the diversity of aniline degraders and the environments they inhabit, and provide guidance related to the bioremediation of aniline contaminated sites with complex pH environments.

Desulfatiglans anilini Initiates Degradation of Aniline With the Production of Phenylphosphoamidate and 4-Aminobenzoate as Intermediates Through Synthases and Carboxylases From Different Gene Clusters

The anaerobic degradation of aniline was studied in the sulfate-reducing bacterium Desulfatiglans anilini. Our aim was to identify the genes and their proteins that are required for the initial activation of aniline as well as to characterize intermediates of this reaction. Aniline-induced genes were revealed by comparison of the proteomes of D. anilini grown with different substrates (aniline, 4-aminobenzoate, phenol, and benzoate). Most genes encoding proteins that were highly abundant in aniline- or 4-aminobenzoate-grown D. anilini cells but not in phenol- or benzoate-grown cells were located in the putative gene clusters ani (aniline degradation), hcr (4-hydroxybenzoyl-CoA reductase) and phe (phenol degradation). Of these putative gene clusters, only the phe gene cluster has been studied previously. Based on the differential proteome analysis, four candidate genes coding for kinase subunits and carboxylase subunits were suspected to be responsible for the initial conversion of aniline to 4-aminobenzoate. These genes were cloned and overproduced in E. coli. The recombinant proteins were obtained in inclusion bodies but could be refolded successfully. Two subunits of phenylphosphoamidate synthase and two carboxylase subunits converted aniline to 4-aminobenzoate with phenylphosphoamidate as intermediate under consumption of ATP. Only when both carboxylase subunits, one from gene cluster ani and the other from gene cluster phe, were combined, phenylphosphoamidate was converted to 4-aminobenzoate in vitro, with Mn²⁺, K⁺, and FMN as co-factors. Thus, aniline is degraded by the anaerobic bacterium D. anilini only by recruiting genes for the enzymatic machinery from different gene clusters. We conclude, that D. anilini carboxylates aniline to 4-aminobenzoate via phenylphosphoamidate as an energy rich intermediate analogous to the degradation of phenol to 4-hydroxybenzoate via phenylphosphate.

Remedial Technologies for Aniline and Aniline Derivatives Elimination from Wastewater

BACKGROUND

Aniline and its derivatives are widely used as intermediate chemicals in the pharmaceutical and dye industries and are present in their wastewaters. These chemicals are of concern due to their potential detrimental effects on public health and aquatic species in the environment.

OBJECTIVES

Various available remedial technologies presented in the literature were investigated to determine the most suitable technology for the elimination of aniline and aniline derivatives from waste streams.

METHODS

The related literature was collected electronically from ScienceDirect, Google Scholar, the International Agency for Research on Cancer (IARC), ResearchGate and Wiley Online Library for systematic review. The search terms included 'aniline', 'aniline degradation', 'advanced oxidation processes (AOPs)', 'aniline derivatives' and 'Fenton's reagent'.

DISCUSSION

Aniline and its derivatives are a serious issue in the effluents of dye and pharmaceutical industries, but a number of efficient treatment methods using biological, physical and AOPs have been presented in the literature.

CONCLUSIONS

Comparison of the available technologies showed that AOPs were the most cost effective and efficient technologies for eliminating aniline and its derivatives from wastewater.

COMPETING INTERESTS

The authors declare no competing financial interests.

Effects of glucose and starch on the toxicity of nitrobenzene to plants and microbes in constructed wetlands

Photosynthetic pigment content, antioxidant enzyme activities of plants, microbial enzyme activities and community structure were analyzed to investigate the effects of glucose and starch on the toxicity of nitrobenzene (NB) to plants and microbes in constructed wetlands (CWs). As the influent NB concentration increased from 10 mg/L to 100 mg/L, the NB removal efficiency of the blank group decreased from 97.1% to 75.02%. However, the NB removal efficiencies of the external carbon source groups were maintained at nearly 100%. External carbon sources accelerated the transformation process of NB to aniline (AN), thus decreasing NB toxicity to the microbes and plants. When the influent NB concentration reached 100 mg/L, the NB removal rates and NB reductase activities of the external carbon source groups were 2.4 times and 4 times higher, respectively, than those of the blank group. Most of the dominant genera found in the three CWs could reduce nitroaromatics to the corresponding aromatic amines according to the results of high-throughput sequencing. The performance of NB removal in the CWs indicated the potential of CWs for NB treatment and the necessity of external carbon sources under high NB concentrations.

Community Structure Analysis and Biodegradation Potential of Aniline-Degrading Bacteria in Biofilters

Aniline has aroused general concern owing to its strong toxicity and widespread distribution in water and soil. In the present study, the bacterial community composition before and after aniline acclimation was investigated. High-throughput Illumina MiSeq sequencing analysis illustrated a large shift in the structure of the bacterial community during the aniline acclimation period. Bacillus, Lactococcus, and Enterococcus were the dominant bacteria in biologically activated carbon before acclimation. However, the proportions of Pseudomonas, Thermomonas, and Acinetobacter increased significantly and several new bacterial taxa appeared after aniline acclimation, indicating that aniline acclimation had a strong impact on the bacterial community structure of biological activated carbon samples. Strain AN-1 accounted for the highest number of colonies on incubation plates and was identified as Acinetobacter sp. according to phylogenetic analysis of the 16S ribosomal ribonucleic acid gene sequence. Strain AN-1 was able to grow on aniline at pH value 4.0-10.0 and showed high aniline-degrading ability at neutral pH.

CATALOGIC 301C model - validation and improvement

In Europe, REACH legislation encourages the use of alternative in silico methods such as (Q)SAR models. According to the recent progress of Chemical Substances Control Law (CSCL) in Japan, (Q)SAR predictions are also utilized as supporting evidence for the assessment of bioaccumulation potential of chemicals along with read across. Currently, the effective use of read across and QSARs is examined for other hazards, including biodegradability. This paper describes the results of external validation and improvement of CATALOGIC 301C model based on more than 1000 tested new chemical substances of the publication schedule under CSCL. CATALOGIC 301C model meets all REACH requirements to be used for biodegradability assessment. The model formalism built on scientific understanding for the microbial degradation of chemicals has a well-defined and transparent applicability domain. The model predictions are adequate for the evaluation of the ready degradability of chemicals.

Effects of nitrogen plasma treatment on the surface characteristics of olive stone-based activated carbon

Nitrogen plasma treatment (NPT) of activated carbon (AC) at different conditions was carried out to introduce nitrogen-containing groups onto olive stone-activated carbon (OSAC) surfaces. Textural characteristics of raw and irradiated samples were analyzed by N₂ and CO₂ adsorption. Surface chemical functional groups were analyzed by X-ray photoelectron spectrometry (XPS) and Fourier Transformed Infrared spectroscopy. The results showed that after NPT, the surface textural properties of irradiated OSAC were slightly damaged, and a gradual decrease in surface area and pore volume was observed during the irradiation. XPS revealed that NPT could change the distribution of oxygen functional groups on the OSAC surface and there were more nitrogen atoms incorporated into the aromatic ring. A tentative explanation for the modification process is proposed. Phenol adsorption was enhanced from 110 mg/g for untreated AC to 635 mg/g for 30-min plasma-treated OSAC.

Simultaneous removal of aniline, nitrogen and phosphorus in aniline-containing wastewater treatment by using sequencing batch reactor

The high removal efficiencies of traditional biological aniline-degrading systems always lead to accumulation of ammonium. In this study, simultaneous removal of aniline, nitrogen and phosphorus in a single sequencing batch reactor was achieved by using anaerobic/aerobic/anoxic (A/O/A) operational process. The removal efficiencies of COD, NH4(+)-N, TN, TP were over 95.80%, 83.03%, 87.13%, 90.95%, respectively in most cases with 250mgL(-1) of initial aniline at 6h cycle when DO was 5.5±0.5mgL(-1). Aniline was able to be completely degraded when initial concentrations were less than 750mgL(-1). When DO increased, the removal rate of NH4(+)-N and TP slightly increased along with the moderate decrease of removal efficiencies of TN. The variation of HRT had obvious influence on removal performance of pollutants. The system showed high removal efficiencies of aniline, COD and nutrients during the variation of operating conditions, which might contribute to disposal of aniline-rich industrial wastewater.

Pathways of nitrobenzene degradation in horizontal subsurface flow constructed wetlands: Effect of intermittent aeration and glucose addition

Intermittent aeration and addition of glucose were applied to horizontal subsurface flow constructed wetlands in order to investigate the effect on pathways of nitrobenzene (NB) degradation and interactions with microbial nitrogen and sulphur transformations. The experiment was carried out in three phases A, B and C consisting of different NB loading and glucose dosing. For each phase, the effect of aeration was assessed by intermittently aerating one wetland and leaving one unaerated. Regardless of whether or not the wetland was aerated, at an influent NB concentration of 140 mg/L, both wetlands significantly reduced NB to less than 2 mg/L, a reduction efficiency of 98%. However, once the influent NB concentration was increased to 280 mg/L, the aerated wetland had a higher removal performance 82% compared to that of the unaerated wetland 71%. Addition of glucose further intensified the NB removal to 95% in the aerated wetlands and 92% in the unaerated. Aeration of wetlands enhanced NB degradation, but also resulted in higher NB volatilization of 6 mg m(-2) d(-1). The detected high concentration of sulphide 20-60 mg/L in the unaerated wetland gave a strong indication that NB may act as an electron donor to sulphate-reducing bacteria, but this should be further investigated. Aeration positively improved NB removal in constructed wetlands, but resulted in higher NB volatilization. Glucose addition induced co-metabolism to enhance NB degradation.

Bacterial degradation of monocyclic aromatic amines

Aromatic amines are an important group of industrial chemicals, which are widely used for manufacturing of dyes, pesticides, drugs, pigments, and other industrial products. These compounds have been considered highly toxic to human beings due to their carcinogenic nature. Three groups of aromatic amines have been recognized: monocyclic, polycyclic, and heterocyclic aromatic amines. Bacterial degradation of several monocyclic aromatic amines has been studied in a variety of bacteria, which utilizes monocyclic aromatic amines as their sole source of carbon and energy. Several degradation pathways have been proposed and the related enzymes and genes have also been characterized. Many reviews have been reviewed toxicity of monocyclic aromatic amines; however, there is lack of review on biodegradation of monocyclic aromatic amines. The aim of this review is to summarize bacterial degradation of monocyclic aromatic amines. This review will increase our current understanding of biochemical and molecular basis of bacterial degradation of monocyclic aromatic amines.

Analysis of biodegradation by-products of nitrobenzene and aniline mixture by a cold-tolerant microbial consortium

A cold-tolerant microbial consortium, which can use nitrobenzene (NB) and aniline (AN) as sole carbon, nitrogen and energy sources, was isolated from an NB and AN contaminated site. Pilot 454 pyrosequencing analysis of the consortium showed that it was mainly made up of Pseudomonas spp. (98%). At 10 °C, the consortium degraded the mixture of 50mg/L NB and 50mg/L AN at a similar rate as those achieved at 20 °C and 30 °C. The biodegradation by-products with different initial NB and AN concentrations at 10 °C were analyzed. Azobenzene, azoxybenzene and acetanilide were observed in NB and AN mixtures degradation. These by-products are generated by the reaction between different intermediates resulting from the NB and AN degradation as well as the parent compounds. To the best of our knowledge, this is the first report confirming the by-products of NB and AN mixture biodegradation by a cold-tolerant microbial consortium.

Efficient bio-deodorization of aniline vapor in a biotrickling filter: metabolic mineralization and bacterial community analysis

A biotrickling filter inoculated with commercial mixed microorganisms B350 was employed to treat N-containing odorous vapor - aniline. Results indicated no aniline could be detected when empty bed residence time (EBRT) was larger than 110s at inlet concentration of 0.30 g m(-3). The variation of inlet concentration did not change removal efficiencies when concentration is less than 0.21 g m(-3) at fixed EBRT 110s. Biodegradation mechanism of aniline was tentatively proposed based on identified intermediates and predicted biodegradation pathway as well as final mineralized products. Aniline was firstly biodegraded to catechol, and then to levulinic acid and subsequently to succinic acid. Finally, about 62% aniline carbon was completely mineralized to CO(2), while about 91% aniline nitrogen was converted into ammonia and nitrate. Bacterial community in biotrickling filter was found that at least seven bands microbes were identified for high efficiencies of bioreactor at stable state. In all, biotrickling filter seeded with B350 would be a better choice for the purification odorous gas containing high concentration aniline.

Synergistic removal of aniline by carbon nanotubes and the enzymes of Delftia sp. XYJ6

Synergistic removal of aniline by carbon nanotubes and the enzymes of Delftia sp. XYJ6, a newly isolated bacterial strain for biodegrading aniline, was investigated. It showed that biodegradation rate of aniline was increased with the augment of protein concentration in cell-free extract of Delftia sp. XYJ6. The adsorption amount of aniline by multi-walled carbon nanotubes (MWCNTs) was slightly higher than that by single-walled carbon nanotubes (SWCNTs), however the adsorption amount of protein of Delftia sp. XYJ6 by MWCNTs was lower than that by SWCNTs. Much more amount of aniline could be removed by CE of Delftia sp. XYJ6 in the presence of SWCNTs than MWCNTs, which indicated that an efficient reaction between aniline and enzymes of Delftia sp. XYJ6 on the surface of SWCNTs played a key role in the rapid enzymatic biodegradation of aniline. This study is not previously reported and may be useful in basic research and the removal of aniline from wastewater.

Biodegradation of aniline by Candida tropicalis AN1 isolated from aerobic granular sludge

Aniline-degrading microbes were cultivated and acclimated with the initial activated sludge collected from a chemical wastewater treatment plant. During the acclimation processes, aerobic granular sludge being able to effectively degrade aniline was successfully formed, from which a preponderant bacterial strain was isolated and named as AN1. Effects of factors including pH, temperature, and second carbon/nitrogen source on the biodegradation of aniline were investigated. Results showed that the optimal conditions for the biodegradation of aniline by the strain AN1 were at pH 7.0 and 28-35 degrees C. At the optimal pH and temperature, the biodegradation rate of aniline could reach as high as 17.8 mg/(L x hr) when the initial aniline concentration was 400 mg/L. Further studies revealed that the addition of 1 g/L glucose or ammonium chloride as a second carbon or nitrogen source could slightly enhance the biodegradation efficiency from 93.0% to 95.1%-98.5%. However, even more addition of glucose or ammonium could not further enhance the biodegradation process but delayed the biodegradation of aniline by the strain AN1. Based on morphological and physiological characteristics as well as the phylogenetic analysis of 26S rDNA sequences, the strain AN1 was identified as Candida tropicalis.

Aniline-induced tryptophan production and identification of indole derivatives from three purple bacteria

Growth on aniline by three purple non-sulfur bacteria (Rhodospirillum rubrum ATCC 11170, Rhodobacter sphaeroides DSM 158, and Rubrivivax benzoatiliticus JA2) as nitrogen, or carbon source could not be demonstrated. However in its presence, production of indole derivatives was observed with all the strains tested. At least 14 chromatographically (HPLC) distinct peaks were observed at the absorption maxima of 275-280 nm from aniline induced cultures. Five major indoles were identified based on HPLC and LC-MS/MS analysis. While tryptophan was the major common metabolite for all the three aniline induced cultures, production of indole-3-acetic acid was observed with Rvi. benzoatilyticus JA2 alone, while indole-3-aldehyde was identified from Rvi. benzoatilyticus JA2 and Rba. sphaeroides DSM 158. Indole-3-ethanol was identified only from Rsp. rubrum ATCC 1170 and anthranilic acid was identified from Rba. sphaeroides DSM 158.